Expansion of a GGGGCC hexanucleotide sequence within the intron of the human C9ORF72 gene is associated with both amyotrophic lateral sclerosis and frontotemporal dementia in humans. Amyotrophic lateral sclerosis (ALS) is a debilitating disease with varied etiology characterized by rapidly progressing weakness, muscle atrophy, muscle spasticity, difficulty speaking (dysarthria), difficulty swallowing (dysphagia), and difficulty breathing (dyspnea). Although the order and rate of symptoms varies from person to person, eventually most subjects are not able to walk, get out of bed on their own, or use their hands and arms. Most subjects with ALS will eventually die from respiratory failure, usually within three to five years from the onset of symptoms. Riluzole (Rilutek) is the only currently available treatment for ALS and only slows progression and increases survival to a modest extent. Frontotemporal dementia (FTD) is also a devestating group of disorders resulting from atrophy or shrinkage of the frontal and temporal lobes of the brain. This shrinkage or atrophy results in severe behavioral changes. There is currently no cure for FTD and limited medications for managing the symptoms of FTD. New methods for diagnosing and treating ALS and/or FTD would greatly benefit ALS and FTD subjects.